A mail stacker is usually a part of a mailing machine, addressing equipment or mail creation equipment. Mail stackers can be classified into two types: top stackers and bottom stackers. In a top stacker, a later mail piece is stacked on top of the earlier ones. In a bottom stacker, a later mail piece is placed at the bottom part of the stack. In some applications such as addressing and inserting systems, mail pieces are required to be stacked in a certain serial order. For example, mail pieces are required to be stacked in a forward serial order in order to be eligible for a postal discount. The addressing information is often printed on top of the mail pieces.
For mail pieces printed in a 1-to-N order, the topmost mail piece in a mail stack having a forward serial order is always printed earlier than the rest of the stack. However, top stackers will reverse the order of the mail pieces to an N-to-1 order while stacking. In order to keep a forward serial order when using a top stacker, an application software can be used to reverse the serial order when addressing. The use of order-reversing software adds considerable complexity to the mail processing system, especially for jam recovery.
Thus, in a mail system requiring a forward serial order, it is advantageous and desirable to use a bottom stacker to reverse the serial order while stacking.
Bottom stackers are known in the art. For example, Keane et al. (U.S. Pat. No. 6,398,204 B1) discloses a belt stacker wherein mail pieces are separately fed by an edge feeder to a stacking deck on the edge of the stacker at the upstream end of the stacking deck. The mail pieces already in the stack are moved by a conveyer belt toward the downstream, away from the edge feeder. At the same time, a stack support is used to keep the stacked mail pieces in an upright position while they are moved downstream. The stack support must be moved toward the downstream end to allow additional room for the stack to grow. In Keane et al., the stack support is either manually relocated or moved by the conveyor belt. Marsullo et al. (U.S. Pat. No. 5,709,525) also discloses a bottom stacker, wherein a pusher mechanism is used for sealing the incoming envelope and pushing the sealed envelope onto a horizontal deck for stacking. In order to keep the stacked envelope in an upright position, a stack support is placed on top of the stack. The stack support is urged by a spring disposed on the back side of the stack support against a rear wall of the stacking deck.
This type of bottom stacker requires a large footprint in that the size of the stacker is determined mainly by the size of the stack, and not the size of the mail pieces in the stack.
It is thus advantageous and desirable to provide a method for stacking the mail pieces in a forward serial order without requiring a large stacker footprint. Furthermore, the mail pieces in a stack can be easily unloaded.